Method of forming insulator bodies



Patented Apr. 11, 1944 METHOD OF FORMING INSULATOR BODIES Edward M. Skipper, Baltimore, Md., assignor to Locke Insulator Corporation, Baltimore, Md, a corporation of Maryland .No Drawing. Application November 28, 1940, Serial No. 367,673

6 Claims.

This invention relates to the production of high tension insulators and more particularly to a method by which the clay is prepared for subsequent formation of the insulator body.

One of the principal objects of the invention, generally considered, is to provide a method of which scrap material resulting from the turning of insulator bodies or the formation of grooves or recesses therein may be quickly utilized without extensive retreatment and, in numerous instances, without any retreatment in the formation of pugs from which the insulator bodies may be formed.

A still further object of the invention is to provide means for materially reducing the time required to dry insulator bodies prior to firing of the same, that is the reduction of the time interval which, up to the present time, has always elapsed between the formation of the insulator body and the firing of the same.

Still another object of the invention is to provide insulator body material in which the shrinkage of the clay from the formation of the pug to the completion of the fired insulator has been reduced to substantially one-eighth of the usual shrinkage from ordinary pugged clay to the finished product.

Still another object of my invention is to provide a method whereby either pulverized bone dry scrap or pulverized raw materials may be mixed with approximately twelve percent (12%) water and immediately, thereafter pugged to form insulator blanks without any intermediate processing.

Still another object of my invention is to provide a method whereby leather-dry scrap may be directly fed into a suitable pug mill and combined therein with other clay masses without previously having to undergo certain preliminary processing.

To these and other ends, the invention resides in the method hereinafter described, the novel features thereof being set forth in the appended claims.

In the production of porcelain clay the raw materials, generally flint, feldspar, ball clay and china clay, are ground or pulverized in ball mills, are then mixed with an excess of water, and are then strained, blunged and filtered, the filtering operation taking place in the usual filter bags under pressure to form a filter cake. After the cake has hardened to a certain point, which step requires a number of hours, it is removed from the filter bag and placed in a pug-mill and thepugextruded therefrom is cut into suitable lengths. These clay pieces or pugs may be formed into insulators directly by filling the openings in plaster of Paris molds with suitable clay portions and subjecting the clay thus held to the rapidly rotating die member of a centering machine to form therein the underneath surface conformation of the finished insulator.

Entrance bushings and other forms of high tension insulators of the post or rod type may be, and preferably are, formed from suitable lengths of such clay pugs by turning. In the formation of such insulators the cut pugs having the desired center openings are permitted to dry, preferably in a trough or wedge-shaped receptacle until the same have reached either the leather or the bone-dry state, the actual drying time being dependent upon many factors such as size, shape, location and air temperature.

When the insulator blanks have arrived at the so-called leather-dry state they may be either rotated in a lathe or on the equivalent of a potters wheel so as to permit the formation therein of undercut grooves or recesses or, in the case of bushings, to form, during rotation of the blank preferably in a horizontal plane, the undercut petticoats, skirt portions or ridges as desired. The blanks may also be allowed to continue to dry until they are in the bone-dry state, that is their moisture content is less than 3% and then cut or ground to the desired shape and size.

A large mass of the clay body is cut away when the blank is operated upon in the leatherdry state in order to produce the finished article and these cuttings create a serious problem in any well organized insulator plant, since, in order for the plant to re-use the same, it has, heretofore, been necessary that they be first dried and then pulverized or ground and then again mixed with water and sent through the regular process.

In addition to the so-called leather-dry scrap there is often a large number of unfired insulator bodies which, owing to defects, are thrown into the scrap pile and it has been customary to regrind such material, after it has been thoroughly dried, by the use of a ball mill and the material so produced is then subjected to the various steps outlined above, the number and order of the steps of course being largely dependent upon the ultimate product of the plant and the processes used in the mixing of this ultimate product. I have found, however, that clay bodies can be reduced to a pulverized trapped air.

mass by grinding the same in a mulling machine and after or during such grinding a desired amount of moisture can be added so there can be produced from the mulling machine or dry mixer a thoroughly mixed and homogeneous clay in the form of a granular mass having a moisture content of from approximately ten percent to approximately twenty-two and one-half percent (22 The clays having a moisture content of between twenty-one percent (21%) and twentytwo and one-half percent (22 /2%) are soft clays which can be immediately introduced into the ordinary pug mill and extruded therefrom in the form of pugs from which suitable portions are/cut to form insulator blanks or the cut portions may be used with plaster of Paris molds, as heretofore described, in combination with centering machines or presses to form pin type or suspension insulators.

The medium hard clays, that is those clays which have a moisture content below twenty-one percent (21%) and above fourteen percent (14%) can be immediately introduced into a hard'pug mill, that is a pug mill in which the pressure applied may run as high as fifty tons per square inch and the pugs extruded from such machines are immediately available for turning operations and require no intermediate drying processes.

,, The hard clays, that is those clays of approximately twelve percent (12%) moisturecontent,

may be introduced into the hard pug mill and exattached thereto, an open trough in which is rotating a shaft provided with a series of knives,

the angle of advance of which is such as to cause the clay to be progressively moved into the hopper of the pug mill. The hopper of the mill is ,p'rovided with the usual shaft having blades thereon to force the clay in a continuous mass through the orifice of the hopper into the nozzle .portion of the mill at which point it is subjected t'oja'high vacuum to remove therefrom any en- The nozzle portion of the pug mill is provided, as usual, with an extrusion screw although, owing to the vastly greater density of the clay, the power applied to the extrusion screw 'is' greatly increased over the ordinary or soft pug mill and I have found it advisable, in order to prevent the friction of the moving clay caused By the use of the apparatus described it is not only possible to immediately re-use the leather-dry scrap but to also use the bone-dry product after the same has been pulverized in the mulling machine and it is also possible, by directly mixing the dry ingredients such as flint, feldspar, ball clay and china clay in the mulling machine and then adding the requisite amount of water, to produce in this single operation a clay mass of any desired water content between ten percent (10%) and twenty-two percent (22%).

Not only is it possible to use, as above described, both the leather dry scrap and the bone dry product after the same have been pulverized in V the mulling machine, but it is possible, by introducing the leather dry scrap into the hopper of the hard pug mill, to produce either semihard or hard pugs by the use of leather dry scrap alone or by mixing in the mixing trough connected with the hard pug mill suitable portions of leather dry scrap and product of the mulling machine to either increase or decrease the moisture content of the mass prior to its introduction into the hopper ofthe pug mill.

I have found that approximately ninety percent of the clay body shrinkage-occurs in the period in which the moisture content drops from twenty-two percent (22%) to approximately twelve percent (12%) and that clay bodies containing between elevent percent (11%) and thirteen percent (13%) shrinkonly approximately one-eighth of the total shrinkage of blanks containing approximately twenty-two percent (22%) moisture content. When the clay body contains approximately three percent (3%) moisture contentit is in the bone-dry'state and may then be fired without fear of breakage due to thermal action upon its moisture content."Insulator bodies, when'formed from clay produced as herein described, have such a low moisture content that the time interval between their production and firing is very small compared with the usual drying time of insulators produced by other methods. In fact it is possiblet'o fire the insulators produced-by my process within a few hours after the same are formed. I can, there-- fore, eliminate tying up large sections of the plant by freeing the driers at the end of a few hours so that the driers as now constructed can handle from six to eight times the number of insulators formed byv my improved process over that whichsuch driers could handle were the insulators formed as has been customary in the past. V

By positioning the clay cutting or insulator forming machine at a point adjacent theclelivery of the hard pug or insulator blanks it is possible to deliver the blanks directly to the cutting machine and since, as pointed out above, the shrinkage in the clay having approximately twelve percent (12%) moisture content is approximately only one-eighth the normal shrinkage of clay of twenty-two percent (22%) moisture content, there will be only approximately one percent (1%) shrinkage of the material from the time of its delivery from the pug mill to the finished fired product. Hence it is possible to form the finished insulator without the delay caused by a drying period and with the certain knowledge that the maximum shrinkage of the insulator so formed through the ultimatefirlng step will not be more than approximately one percent (1%).

Not only does my invention therefore. free large sections of the plant for other apparatus by decreasing the area necessary fontherdriers butalso reduces the area of the plantgnormally used to hold all scrap clay to await its full drying before any attempt is made to re-use the same. I have also found that in the production of thimbles and the like from the material pugged from the new type of mill I have greatly decreased the normal loss which runs often as high as forty percent (40%) and find that in like devices produced by my new process the total loss is less than five percent It is believed advisable to again emphasize the fact that clay having approximately twelve percent (12%) moisture content will not shrink appreciably from its finished dimension either during the remaining drying stage or during the subsequent firing. The result is, therefore, that clay produced by the improved pug mill herein described can be brought to approximately finished dimensions with the certainty that but very small allowance need be made during the firing state for shrinkage.

A still further advantage of the invention as herein described resides in the fact that small insulators can be immediately worked as soon as the blank is pugged and that they can be glazed and fired within from four to six hours of production.

It is of importance to note that in the normal processing of porcelain clay ingredients and the production therefrom of the usual filter cake that the central portion of the filter cake dries at a much slower rate than the marginal portion and it is therefore essential, before introduction of the filter cake into the soft pug mill, to remove from the filter cake the soft central portion. The removed portion approximates thirty percent (30%) of the total filter cake and consequently there is a scrap loss in the ordinary process of approximately thirty percent (30%) in this step of the process alone, and this scrap may be used after a small amount of drying either in the mulling machine or directly in the hard pug mill, thus entirely eliminating this heavy loss.

I have, therefore, by my invention, first, reduced the cost of producing insulator body material; second, reduced the time; third, reduced the loss figure; and, fourth, released a large amount of space in plant operation so that other and more advantageous types of machines may be substituted for the drying racks or other types of driers, as the case may be, and have further released the space generally used to store the clay scrap to await its driving.

Since the apparatus described is readily obtainable on the open market and since my invention does not relate to the apparatus it is believed unnecessary for a clear understanding of the invention to illustrate the apparatus herein described.

Whenever in the claims the expression unfired porcelain is used, it is to be understood that this expression is intended to cover either scrap material as herein described or raw material to which, after thorough mixing, a definite water percentage has been added.

Having thus described my invention, what I claim is:

1. The method of producing high tension insulator bodies, which includes simultaneously mixing unfired porcelain clay ingredients including scrap clay with suificient water t giv t the mixture a water content of between eleven percent (11%) and thirteen percent (13%), jn troducing the mixed mass into a high pre sure pug mill, extruding said product, and final'i shaping selected portions thereof to produce thelgfrom high tension insulator bodies.

2. The method of producing high tension m lator bodies which includes simultaneously mix. ing unfired porcelain clay ingredients including scrap clay with sufiicient water to give to the said mixture a water content of between eleven percent (l1%) and thirteen percent (13%), introducing the mixed mass into a, high pressure pug mill, extrudin said product, immediately shaping selected portions thereof to produce therefrom high tension insulator bodies, glazing said bodies, and finally firing the same.

3. The method of producing high tension insulator blanks comprising introducing into the pan of a mulling machine unfired bone-dry porcelain clay material mixed with leather dry scrap, adding to said mixture an amount of water sufficient to provide said mixture with a, given percentage of moisture, causing said machine to operate to form therefrom a homogeneous clay mix, removing said mass from the machine, and finally subjecting portions of said mass to pressure to form said blanks.

4. The method of producing high tension insulator blanks comprising introducin into the pan of a mulling machine unfired porcelain clay ma terial comprising bone dry scrap, adding to said mixture an amount of water sumcient to provide said mixture with a given precentage of moisture, causing said machine to operate to form therefrom a homogeneous clay mixture removing said mass from the machine, and finally subjecting portions of said mass to pressure to form said blanks.

5. The method of producing high tension insulator blanks comprisin introducing into the pan of a mulling machine unfired porcelain clay material, mixed with leather dry and bone dry scrap, adding to said mixture an amount of water sufficient to provide said mixture with a given percentage of moisture, causing said machine to operate to form therefrom a homogeneous clay mixture, removing said mass from the machine, and finally subjecting portions 01 said mass to pressure to form said blanks.

6. The method of producing high tension insulator blanks comprising introducing into the pan of a mulling machine unfired porcelain clay material including bone dry scrap, adding to said mixture an amount of water sufiicient to providesaid mixture with a given percentage of moisture ranging between eleven percent (11%) and sixteen percent (16%), causing said machine to operate to form therefrom a homogeneous clay mixture, removing said mass from the mulling machine, introducing said mass into a high pressure pug mill, and finally subjecting portions of the extruded product of said mill to pressure to form said blanks.

EDWARD M. SKIPPER. 

